This invention relates to the polymerization of ethylene at high pressures.
It is well known that polymerization or copolymerization of ethylene can be effected at high pressure in the presence of either a free-radical yielding catalyst or a catalyst comprising a transition metal compound. In a typical continuous high pressure process, the reactant mixture in the polymerization reactor is under super-critical conditions and is passed to a separator at lower pressure in which the polymer separates from a large proportions of the gas. The polymer is then passed to a hopper at a lower pressure than the separator. The major part of the gas which remains dissolved in the polymer is removed in the hopper and the polymer is then passed to an extruder. The gas removed from the polymer in the hopper is recompressed, mixed with the gas from the separator, make-up ethylene (and comonomer) as required, compressed further and returned to the polymerization reactor. If polymerization is effected in a multizone reactor, a proportion of the feed gas may be introduced into each zone.
U.S. Pat. No. 4,014,859 describes a process for the polymerization of ethylene in at least two reaction zones comprising the particular feature of passing the gas from the separator to at least one zone other than the first zone of the polymerization reactor. It may be observed however that the process results in polymer deposits in the first zone of the reactor, which do not permit the necessary maintenance of a single phase in the first zone.